An image sensor is a semiconductor device capable of sensing external light and converting it into an electrical signal. Current integrated circuit (IC) processes allow hundreds or even thousands of image sensor dies to be formed on the same wafer. These image sensor dies are then packaged into image sensor packages, bonded with terminal leads onto their metal pads and provided with lenses and lens holders to form lens modules which can be used in cameras, smart phones, digital cameras, automotive imaging systems, toys and other electronic devices.
A commonly-used conventional image sensor packaging method is known as chip-on-board (COB) packaging in which image sensor dies are bonded onto an printed circuit board (typically, a PCB) with a conductive or non-conductive adhesive and then wire bonding is carried out for their electrical connections. Subsequently, micro lens of the image sensor dies are provided with micro lenses surfaces, for example, by epoxy resin.
FIG. 1 schematically illustrates a cross section of an image sensor package resulting from a conventional COB packaging process. As shown in FIG. 1, the image sensor package includes, along a direction perpendicular to micro lens surfaces 11 of image sensor dies 10 (i.e., the areas for reception of external light and for photoelectric conversion), a PCB board 15, the image sensor dies 10 (each including a substrate 12, the micro lens surface 11 and the metal pads 13), a protective layer 14 (such as an anti-reflection layer and has a material of SiO2) over the micro lens surfaces 11 and metal leads 17 connecting the metal pads 13 to the PCB board 15. On the one hand, since the image sensor dies 10 reside on the PCB board 15, the sensor package has a relative great thickness (i.e., its longitudinal dimension as viewed in FIG. 1). On the other hand, the metal leads 17 are typically bonded to the metal pads 13 and the PCB board 15 by wire bonding, which usually requires the metal pads 13 to be spaced from the micro lens surfaces 11 by a distance d of 500 μm or larger (with respect to a direction parallel to the micro lens surface 11) due to process constraints. This is unfavorable to further shrinkage of the image sensor package. Moreover, these two disadvantages can both lead to dimensional limitations to the subsequent construction of a lens module from the package of FIG. 1.